Triptolide derivatives for modulation of apoptosis and immunosuppression

ABSTRACT

Variously substituted carbonate and carbamate derivatives of triptolide compounds have good aqueous solubility and convert to biologically active compounds in vivo, at a rate which can be modulated by varying the substitution on the prodrug. The prodrugs are useful as immunosuppressive, anti-inflammatory and anticancer agents.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of currently pending U.S.application Ser. No. 10/478,777, a 35 U.S.C. §371 National Stage ofInternational Application No. PCT/US03/17177, filed 29 May 2003, whichclaims the benefit under 35 U.S.C. §119(e) of Provisional ApplicationNo. 60/384,480, filed 31 May 2002, the contents of each of which areexpressly incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to prodrugs useful as immunosuppressive,anti-inflammatory and anticancer agents, and methods of their use. Thecompounds have good aqueous solubility and convert to biologicallyactive compounds in vivo, at a rate which can be modulated by varyingthe substitution on the prodrug.

REFERENCES

-   Bagshawe, K. D. Antibody directed enzymes revive anti-cancer    prodrugs concept. Br J Cancer 56:531-532 (1987).-   Bagshawe, K. D. Antibody-directed enzyme prodrug therapy (ADEPT).    Adv Pharmacol. 24:99-121 (1993).-   Bagshawe, K. D, Springer, C. J., Searle, F., Antoniw, P., Sharma, S.    K., Melton, R. G., Sherwood R F. A cytotoxic agent can be generated    selectively at cancer sites. Br J Cancer 58:700-703 (1988).-   Bagshawe, K. D. Towards generating cytotoxic agents at cancer sites.    Br J Cancer 60:275-281 (1989).-   Boyd, G. V. and Heatherington, K., J. Chem. Soc. Perkin I 2523-2531    (1973).-   Ferrier, R. J., in CARBOHYDRATE CHEMISTRY, Kennedy, J. F., Ed.,    Clarendon Press, Oxford (1990).-   Garver, L. C. et al., J. Am. Chem. Soc. 104:867 (1982).-   Gleichmann, E. et al., Immunol. Today 5:324 (1984).-   Hormi, O. E. O. and Nasman, J. H., Syn. Commun. 16:69 (1986).-   Kocienski, P. J., PROTECTING GROUPS, Georg Thieme Verlag, Stuttgart    (1994).-   Korngold, R. and Sprent, J., J. Exp. Med. 148:1687 (1978).-   Kupchan, S. M. et al., J. Am. Chem. Soc. 94:7194 (1972).-   Kupchan, S. M. et al., U.S. Pat. No. 3,005,108 (1977).-   Lipsky, P. E. et al., U.S. Pat. No. 5,294,443 (1994).-   Ma, P-C. et al., J. Chin. Pharm. Sci. 1:12 (1992).-   Mori, S. et al., Tetrahedron 47(27):5051-5070 (1991).-   Morris, R. E., Transplant Proc. 23(6):2722-2724 (1991).-   Morris, R. E. et al., Transplant Proc. 23(1):238-240 (1991).-   Murase, N. et al., Transplantation 55:701 (1993).-   Ono and Lindsey, J. Thor. Cardiovasc. Surg. 57(2):225-29 (1969).-   Pu, L. et al., Zhongguo Yaoli Xuebao 11:76 (1990).-   Wang, J. and Morris, R. E., Transplantation Proc. 23:699 (1991).-   Wentworth. P., Datta, A., Blakey, D., Boyle, T., Partridge, L. J.,    Blackburn, G. M. Proc. Natl. Acad. Sci. USA 93:799-803 (1996).-   Yu et al., Acta Pharmaceutica Sinica 27(11):830-836 (1992).-   Zheng, J. et al., Zhongguo Yixue Kexueyuan Xuebao 13:391 (1991).-   Zheng, J. et al., Zhongguo Yixue Kexueyuan Xuebao 16:24 (1994).

BACKGROUND OF THE INVENTION

Immunosuppressive agents are widely used in the treatment of autoimmunedisease and in treating or preventing transplantation rejection,including the treatment of graft-versus-host disease (GVHD), a conditionin which transplanted marrow cells attack the recipient's cells. Commonimmunosuppressive agents include azathioprine, corticosteroids,cyclophosphamide, methotrexate, 6-mercaptopurine, vincristine, andcyclosporin A. In general, none of these drugs are completely effective,and most are limited by severe toxicity. For example, cyclosporin A, awidely used agent, is significantly toxic to the kidney. In addition,doses needed for effective treatment may increase the patient'ssusceptibility to infection by a variety of opportunistic invaders.

A number of compounds derived from the Chinese medicinal plantTripterygium wilfordii (TW) have been identified as havingimmunosuppressive activity, e.g. in the treatment of autoimmune disease,and in treating or preventing transplantation rejection, including thetreatment of graft-versus-host disease (GVHD), a condition in whichtransplanted marrow cells attack the recipient's cells. See, forexample, coowned U.S. Pat. No. 6,150,539 (Triptolide prodrugs havinghigh aqueous solubility), U.S. Pat. No. 5,962,516 (Immunosuppressivecompounds and methods), U.S. Pat. No. 5,843,452 (Immunotherapycomposition and method), U.S. Pat. No. 5,759,550 (Method for suppressingxenograft rejection), U.S. Pat. No. 5,663,335 (Immunosuppressivecompounds and methods), and U.S. Pat. No. 5,648,376 (Immunosuppressantditerpene compound), all of which are incorporated herein by reference,and references cited therein. Such compounds have also been reported toshow anticancer activity. See, for example, Kupchan et al., 1972, 1977,cited above, as well as co-owned PCT Publication No. WO 02/56835, whichis incorporated herein by reference.

The administration and therapeutic effectiveness of these compounds havebeen limited, however, by their low water solubility. This problem hasbeen addressed by formulating the compounds in mixtures of ethanol andpolyethoxylated castor oil (e.g., “CREMOPHOR EL™”), allowing subsequentdilution in saline for intravenous administration. However, suchformulations have suffered from high toxicity, due to the highconcentration of solubilizing agent required to dissolve thesecompounds. For example, the ratio of solubilizing agent (ethanol plus“CREMOPHOR EL™”) to triptolide in such formulations is typically on theorder of 1000:1 or greater, due to the poor solubility of triptolide(Morris, 1991; Morris et al., 1991). Standardization of dosage amountsis also more problematic with a suspension than with a solution.

It is therefore desirable to provide immunosuppressive compounds havingcomparatively low toxicity and improved water solubility. It is alsodesirable to provide prodrug compounds which are convertible to animmunosuppressive form in vivo at a rate which can be controlled byselection of substituents on the prodrug.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a method of inducing cell death,as in treatment of cancer, particularly in treatment of treatment ofcolon cancer, breast cancer, lung cancer, or prostate cancer. In anotheraspect, the invention provides a method of effecting immunosuppression,as in inhibition of transplant rejection, prevention or treatment ofgraft-versus-host disease, or treatment of an autoimmune disease. Inaccordance with the invention, a subject in need of such treatment istreated with an effective amount of a triptolide prodrug, or apharmaceutically acceptable salt thereof, having the structure I, below,in a pharmaceutically acceptable vehicle.

In the structure I, the variables are defined as follows:

X¹ is OH or OR¹, and X² and X³ are independently OH, OR¹ or H, with theproviso that at least one of X¹, X² and X³ is OR¹, and at least one ofX² and X³ is H; and

OR¹ is O—(C═O)—Z, where Z is selected from the group consisting of:—OR², —O—Y—(C═O)—OR³, —O—Y—NR⁴R⁵, —NR⁴R⁵, —NR³—Y—(C═O)—OR³, and—NR³—Y—NR⁴N⁵;

wherein

Y is a divalent alkyl, alkenyl or alkynyl group having up to six carbonatoms;

R² is selected from alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl,aryl, aralkyl, hydroxyalkyl, alkoxyalkyl, aryloxyalkyl, andacyloxyalkyl;

each R³ is independently selected from hydrogen and R²; and

R⁴ and R⁵ are independently selected from hydrogen, alkyl, alkenyl,alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, hydroxyalkyl,alkoxyalkyl, aryloxyalkyl, and acyloxyalkyl, or R⁴ and R⁵ taken togetherform a 5- to 7-member heterocyclic ring whose ring atoms are selectedfrom the group consisting of carbon, nitrogen, oxygen and sulfur,wherein the ring atoms include at most 3 heteroatoms.

The groups defined as R², R³, R⁴, and R⁵, when selected from alkyl,alkenyl, and alkynyl, preferably have up to six carbon atoms. Whenselected from cycloalkyl or cycloalkenyl, they preferably have 3 to 7,or, for cycloalkenyl, 5 to 7 carbon atoms. When selected from aralkyl,hydroxyalkyl, alkoxyalkyl, aryloxyalkyl, and acyloxyalkyl, the alkylcomponents of these groups preferably have up to six carbon atoms. Inone embodiment, each of these groups is independently selected fromalkyl, aryl, aralkyl, and alkoxyalkyl.

In selected embodiments, X²═X³═H, and Y is —CH₂— or —CH₂CH₂—. In furtherembodiments, OR¹ is selected from the group consisting of O—(C═O)—OR²,O—(C═O)—O—Y—(C═O)—OR³, and O—(C═O)—O—Y—NR⁴R⁵(carbonate derivatives). Inother embodiments, OR¹ is-selected from the group consisting ofO—(C═O)—NR⁴R⁵, O—(C═O)—NR³⁻Y—(C═O)—OR³, andO—(C═O)—NR³—Y—NR⁴N⁵(carbamate derivatives).

These and other objects and features of the invention will become morefully apparent when the following detailed description of the inventionis read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing apoptosis induction by invention compoundPG666 (14-ethyl carbamate), in comparison to triptolide (PG490), its14-succinyl ester (PG490-88), and its 14-glutamyl ester (PG661); seealso Table 3.

FIG. 2 is a graph showing apoptosis induction by invention compoundsPG666 (14-ethyl carbamate), PG671 (14-phenyl carbamate) and PG 672(N-methylpiperazinecarbonyl) (carbamate), in comparison to triptolide(PG490), its 14-succinyl ester (PG490-88), and its 14-glutamyl ester(PG661); see also Table 4.

FIG. 3 is a graph showing apoptosis induction by invention compoundsPG666 (14-ethyl carbamate) and PG688 (14-dimethylaminoethyl carbamate),in comparison to triptolide (PG490) and its 14-succinyl ester(PG490-88); see also Table 5.

FIG. 4 is a graph showing IL-2 inhibition by invention compounds PG666(14-ethyl carbamate) and PG688 (14-dimethylaminoethyl carbamate), incomparison to triptolide (PG490) and its 14-succinyl ester (PG490-88);see also Table 7.

FIG. 5 is a graph showing IL-2 inhibition by invention compounds PG666(14-ethyl carbamate), PG671 (14-phenyl carbamate) and PG672(14-N-methylpiperazinecarbonyl) (carbamate), in comparison to triptolide(PG490), its 14-succinyl ester (PG490-88), and its isoglutamyl ester(PG661); see also Table 8.

DETAILED DESCRIPTION OF THE INVENTION I. Definitions

The terms below have the following meanings unless indicated otherwise.

“Triptolide derivatives” or “triptolide analogs” refers to derivativesof triptolide, 16-hydroxytriptolide, or tripdiolide(2-hydroxytriptolide) which are derivatized at one or more hydroxylgroups.

“Alkyl” refers to a fully saturated acyclic moiety consisting of carbonand hydrogen, which may be linear or branched. Examples of alkyl groupsare methyl, ethyl, n-butyl, t-butyl, n-heptyl, and isopropyl. Generallypreferred are lower alkyl groups, having one to six carbon atoms, asexemplified by methyl, ethyl, n-butyl, i-butyl, t-butyl, isoamyl,n-pentyl, and isopentyl.

“Cycloalkyl” refers to a fully saturated cyclic moiety consisting ofcarbon and hydrogen, having three to eight carbon atoms, preferablythree to six carbons atoms; e.g. cyclopropyl or methylcyclopentyl.“Cycloalkenyl” refers to an unsaturated cyclic moiety consisting ofcarbon and hydrogen, having five to eight carbon atoms, preferably fiveor six carbon atoms.

“Alkenyl” refers to an unsaturated acyclic moiety consisting of carbonand hydrogen, which may be linear or branched, having one or more doublebonds. Generally preferred are lower alkenyl groups, having two to sixcarbon atoms. “Alkynyl” refers to an unsaturated acyclic moietyconsisting of carbon and hydrogen, which may be linear or branched,containing one or more triple bonds. Generally preferred are loweralkynyl groups, having two to six carbon atoms.

“Aryl” refers to a substituted or unsubstituted monovalent aromaticradical, generally having a single ring (e.g., benzene) or two condensedrings (e.g., naphthyl), where monocyclic aryl groups are preferred. Theterm includes heteroaryl groups, which are aromatic ring groups havingone or more nitrogen, oxygen, or sulfur atoms in the ring, such asfuryl, pyrrole, pyridyl, and indole. By “substituted” is meant that oneor more ring hydrogens in the aryl group, preferably one or two ringhydrogens, is replaced with a group preferably selected from fluorine,chlorine, bromine, methyl, ethyl, hydroxy, hydroxymethyl, nitro, amino,methylamino, dimethylamino, methoxy, halomethoxy, and halomethyl.

“Acyloxyalkyl” refers to a substituent of the form —R—O—(C═O)—R′, whereR is alkyl, preferably having up to six carbon atoms, and R′ is selectedfrom alkyl, alkenyl, alkynyl, aryl, and aralkyl, where R′ preferablycomprises lower alkyl, lower alkenyl, or lower alkynyl (i.e. C₂-C₆)groups and monocyclic aryl groups.

“Aralkyl” refers to an alkyl, preferably lower (C₁-C₄, more preferablyC₁-C₂) alkyl, substituent which is further substituted with an arylgroup, preferably a monocyclic aryl group; examples are benzyl andphenethyl. Also included is fluorenylmethyl, a component of the widelyemployed Fmoc (fluorenylmethoxycarbonyl) protecting group.

The term “pharmaceutically acceptable salt” encompasses carboxylatesalts having organic and inorganic cations, such as alkali and alkalineearth metal cations (for example, lithium, sodium, potassium, magnesium,barium and calcium); ammonium; or organic cations, for example,dibenzylammonium, benzylammonium, 2-hydroxyethylammonium,bis(2-hydroxyethyl)ammonium, phenylethylbenzylammonium, dibenzylethylenediammonium, and the like. Other cations encompassed by the above terminclude the protonated form of procaine, quinine andN-methylglucosamine, and the protonated forms of basic amino acids suchas glycine, ornithine, histidine, phenylglycine, lysine, and arginine.

The term also includes salts formed by standard acid-base reactions withbasic groups, such as amino groups, having a counterion derived from anorganic or inorganic acid. Such counterions include chloride, sulfate,phosphate, acetate, succinate, citrate, lactate, maleate, fumarate,palmitate, cholate, glutamate, glutarate, tartrate, stearate,salicylate, methanesulfonate, benzenesulfonate, sorbate, picrate,benzoate, cinnamate, and the like.

For the purposes of the current disclosure, the following numberingscheme is used for triptolide and triptolide analogs:

II. Triptolide Analogs

Compounds as represented by structure I, below, are derivatives oftriptolide having hydrophilic substituents, possess greater watersolubility than the non-derivatized starting compound, and are effectiveto hydrolyze and convert in vivo to the parent compound. The compoundsare useful as prodrugs for immunosuppressive, anti-inflammatory andanticancer applications.

A. Structure

In compounds of formula I:

X¹ is OH or OR¹, and X² and X³ are independently OH, OR¹ or hydrogen,with the proviso that at least one of X¹, X² and X³ is OR¹, and at leastone of X² and X³ is hydrogen.

OR¹ is a carbamate or carbonate group, which may be further substituted,e.g. with an ester or amine. In particular, where OR¹ is represented asO—(C═O)—Z, Z is selected from the group consisting of:

—OR²,

—O—Y—(C═O)—OR³,

—O—Y—NR⁴R⁵,

—NR⁴R⁵,

—NR³—Y—(C═O)—OR³, and

—NR³—Y—NR⁴N⁵,

where Y is a divalent alkyl, alkenyl or alkynyl group having up to sixcarbon atoms; R² is selected from alkyl, alkenyl, alkynyl, cycloalkyl,cycloalkenyl, aryl, aralkyl, hydroxyalkyl, alkoxyalkyl, aryloxyalkyl,and acyloxyalkyl; and each R³ is independently selected from hydrogenand R². R⁴ and R⁵ are independently selected from hydrogen, alkyl,alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, hydroxyalkyl,alkoxyalkyl, aryloxyalkyl, and acyloxyalkyl. Alternatively, R⁴ and R⁵taken together may form a 5- to 7-member heterocyclic ring whose ringatoms are selected from the group consisting of carbon, nitrogen, oxygenand sulfur, where the ring atoms include at most 3 heteroatoms. Examplesinclude, but are not limited to, piperidine, piperazine, pyrrolidine,and morpholine.

The groups defined as R², R³, R⁴, and R⁵, when selected from alkyl,alkenyl, and alkynyl, preferably have up to six carbon atoms. Whenselected from cycloalkyl or cycloalkenyl, they preferably have 3 to 7,or, for cycloalkenyl, 5 to 7 carbon atoms. When selected from aralkyl,hydroxyalkyl, alkoxyalkyl, aryloxyalkyl, and acyloxyalkyl, the alkylcomponents of these groups preferably have up to six carbon atoms. Inone embodiment, each of these groups is independently selected fromalkyl, aryl, aralkyl, and alkoxyalkyl.

In one embodiment, X¹ is OR¹, and each of X² and X³ is hydrogen. Inanother embodiment, Y is methylene (—CH₂—) or ethylene (—CH₂CH₂—).

B. Preparation

The compounds of structure I may be prepared from triptolide, asobtained from the root xylem of the Chinese medicinal plant Tripterygiumwilfordii (TW) or from other known sources. The TW plant is found in theFujiang Province and other southern provinces of China; TW plantmaterial can generally be obtained in China or through commercialsources in the United States. Methods for preparing triptolide and someof its derivatives (e.g. tripdiolide and 16-hydroxytriptolide) are knownin the art and are described, for example, in Kupchan et al. (1972,1977); Lipsky et al. (1994); Pu et al. (1990); and Ma et al. (1992).

The hydroxyl group(s) of triptolide or its derivatives can be convertedto the carbamates of structure I by reaction with an appropriatelysubstituted isocyanate, as shown in Examples 1 (General Procedure A), 5and 6, or by reaction with phosgene and an appropriately substitutedamine, as shown in Examples 2 (General Procedure B) and 7.

Similarly, the hydroxyl group(s) of triptolide or its derivatives can beconverted to the carbonates of structure I by reaction with anappropriately substituted chloroformate, as shown in Examples 3 (GeneralProcedure C), 8 and 9, or by reaction with phosgene and an appropriatelysubstituted alcohol, as shown in Examples 4 (General Procedure D), 10-13and 15. As shown in Examples 7 and 11-15, further functionality on acarbonate or carbamate alkyl group can be incorporated. Metal salts andamine salts are readily prepared by reaction or exchange with anappropriate counterion (Examples 14, 16, 17).

In cases where all available hydroxyl groups on the starting materialare to be derivatized, an excess of reagent can be used to drive thereaction to completion. The compound 16-hydroxytriptolide contains twofree hydroxyl groups, one secondary (at C-14) and one primary (at C-16).Since the hydroxyl group at the 16-position is more reactive than the14-hydroxyl group for steric reasons, mono- and diester derivatives canbe selectively made using appropriate reaction conditions. Reaction witha stoichiometric amount of a selected reagent yields primarily thecompound monoderivatized at the 16-position, with the 14-hydroxyl groupremaining free. Monoderivatives substituted at the more hindered(secondary) hydroxyl group can be prepared by first selectivelyprotecting the less hindered (primary) hydroxyl group, carrying out thederivatization at the unprotected position, and then removing theprotecting group. Suitable hydroxyl protecting groups are well known,and are described, for example, by Kocienski (1994).

Various compounds of the invention, prepared as described above and inthe Examples, are given in the Table below. All are substituted at the14-hydroxyl of triptolide with a carbonate or carbamate substituent.Also included are reference ester substituted compounds, PC490-88 andPG661, as well as the parent compound, designated herein as PG490.

TABLE 1 Exemplary Carbamate- and Carbonate-Substituted TriptolideDerivatives Designation Name (Triptolide derivative) 14-O—(C═O)Xsubstituent Controls PG490 Triptolide PG490-88 14-succinyl esterCH₂CH₂COOH PG661 14-isoglutamyl ester CH₂CH₂CH(NH₂)COOH Compounds PG66614-ethyl carbamate NHCH₂CH₃ PG671 14-phenyl carbamate NH(C₆H₅) PG672N-methylpiperazinecarbonyl (carbamate)

PG674 14-ethyl carbonate OCH₂CH₃ PG676 14-phenyl carbonate O(C₆H₅) PG67914-ethoxyethyl carbonate OCH₂CH₂OCH₂CH₃ PG680 14-methoxycarbonylmethylOCH₂(C═O)OCH₃ carbonate PG681 14-(R)-α-methyl-tert-OC*H(CH₃)(C═O)OC(CH₃)₃ butoxycarbonylmethyl carbonate PG68214-dimethylaminoethyl OCH₂CH₂N(CH₃)₂ carbonate PG682 PTSA14-dimethylaminoethyl OCH₂CH₂N⁺H(CH₃)₂ ⁻OTs carbonate,p-toluenesulfonate salt PG687 14-hydroxycarbonylmethyl OCH₂COOHcarbonate PG687 Na 14-hydroxycarbonylmethyl OCH₂COO⁻⁺Na carbonate,sodium salt PG687 tris 14-hydroxycarbonylmethyl OCH₂COO⁻ ⁺NH₃C(CH₂OH)₃carbonate, tris(hydroxy- methyl)aminomethane salt PG68814-dimethylaminoethyl NHCH₂CH₂N(CH₃)₂ carbamate PG695 14-tert-butylcarbonate OC(CH₃)₃

III. Prodrug Conversion and Apoptosis Inducing Activity

A. Conversion Assays

The compounds of formula I provide the advantage of different andsometimes widely varying rates of conversion to parent compound, asdemonstrated below. Accordingly, prodrugs of formula I can be selectedfor different desired conversion rates in human serum/plasma by choosingdifferent structural constituents linked via a carbonate or carbamatelinkage to triptolide.

Compounds of formula I, as shown in Table 1 above and in the Examples,were assayed for their capacity to induce apoptosis in cells from theJurkat human T lymphocyte cell line, after incubation with pooled humanserum for varying periods of time at 37° C. (see Example 19). An esterprodrug, triptolide-14-succinate, designated PG490-88, was included forcomparison. The extent of conversion to triptolide after such incubationwas also independently determined by HPLC analysis.

The results of the apoptosis assay are presented in Table 2. The ED₅₀values (column 3) are calculated directly from the data in eachexperiment, and the % conversion values (column 4) are calculated aspercent of the ED₅₀ value produced by triptolide, designated PG490,incubated in the same plasma (i.e. in the same experiment). Thisprocedure gives the most valid direct comparison of each compound totriptolide under the same experimental conditions.

Comparison of the percent conversion at each of the incubation timesshows a broad range of values among the compounds. The percentconversion varied from 7% (PG681;14-(R)-α-methyl-tert-butoxycarbonylmethyl carbonate) to 98% (PG674;14-ethyl carbonate) after 1 hour, and from 6% (PG687-tris;14-hydroxycarbonylmethyl carbonate, tris salt) to 100% (PG674, PG695;14-tert-butyl carbonate) or greater (PG682; 14-dimethylaminoethylcarbonate, calculated as >100% compared to PG490) after 48 hours.

TABLE 2 ED₅₀ (nM) Conversion, Incubation in apoptosis as relative Timein assay after ED₅₀ compared t_(1/2) in human Serum incubation totriptolide plasma (min) Cmpd. (hours) with serum (%) by HPLC ControlPG490-88 0.5 2584 2 max. 26% PG490-88 1 2268 2 conversion PG490-88 24328 18 at 48 hr PG490-88 48 147 43 (Na salt) Compounds PG674 0.5 27 18812 PG674 1 55 98 PG674 24 60 97 PG674 48 65 100 PG676 48 56 96 15 PG6790.5 39 128 11 PG680 48 58 85 9 PG681 1 684 7 max. 20% PG681 48 139 40conversion at 48 hr PG682 1 66 76 n.d. PG682 48 32 146 PG682PTSA 1 57 8917 PG687tris 48 960 6 max. 10% at 48 hr (Na salt) PG695 48 59 100 n.d.

Prodrug conversions to triptolide as determined independently by HPLCare given in column 4. As with the bioassay data, a comparison of thet_(1/2) values for conversion to triptolide shows a broad range ofvalues among the compounds. The t_(1/2) values range from 9 minutes(PG680; 14-methoxycarbonylmethyl carbonate), 11 minutes (PG679;14-ethoxyethyl carbonate) and 12 minutes (PG674; 14-ethyl carbonate) toincomplete conversion (10%) in 48 hours of incubation (PG687Na;14-hydroxycarbonylmethyl carbonate, sodium salt). PG681(14-(R)-α-methyl-tert-butoxycarbonylmethyl carbonate), which exhibitsthe lowest percent conversion in the bioassay (7%), convertsincompletely (20%) in 48 hours as assessed by HPLC. PG687(14-hydroxycarbonylmethyl carbonate) converts only 6% within 48 hourswhen evaluated in the apoptosis assay, and only 10% in this time spanwhen assayed by HPLC. PG674 (14-ethyl carbonate) converts 98% in 1 hourand 100% in 48 hours in the bioassay, and exhibits a t_(1/2) of 12minutes by HPLC analysis. PG682 (14-dimethylaminoethyl carbonate)displays conversion calculated as >100% in is apoptosis induction, and a17 minute t_(1/2) by HPLC evaluation.

There is a large measure of consistency between the results of prodrugconversion in human serum to a biologically active, apoptosis-inducingcompound (presumably triptolide) and the conversion in human plasma andexpressed in minutes as the t_(1/2) of prodrug conversion to triptolideassessed by HPLC. There is a broad range of values for the conversion ofprodrugs, whether the conversion is evaluated in the apoptosis inductionbioassay or by HPLC identification and quantification of triptolide.This broad range of conversion values in human serum or plasma indicatesthat the compounds of formula I do not share a similar conversion rateunder these circumstances. This unexpected difference in conversionrates from these triptolide prodrugs to triptolide shows that differentand widely varying rates of conversion can be obtained by makingdifferently substituted prodrugs as described herein.

In general, the carbamate derivatives of the invention, as a class, werefound to convert in human serum less readily than the carbonatederivatives, as a class. As discussed further below, derivatives whichare resistant to hydrolysis by human esterases and proteases may beuseful in antibody directed enzyme prodrug therapy.

B. Dose-Response Data

Dose-response data on apoptosis induction by invention compound PG666(14-ethyl carbamate), in comparison to triptolide (PG490), its14-succinyl ester (PG490-88), and its 14-glutamyl ester (PG661), isgiven in Table 3. The dose-response data is also represented graphicallyin FIG. 1.

TABLE 3 Apoptotic Induction by Triptolide Esters and Carbamate PG666 inthe Presence of Human Serum % apoptotic cells at given concentration(nM) 1 3 10 30 100 300 1000 3000 10000 Human serum, 48 hr PG490 (cntrl) 8.5  8.5  8.5 26.2 91.7 93.4 94.6 95.2 95.4 PG490-88 (cntrl)  7.8  8.1 7.8  9.1 51.5 92.1 93.9 94.1 95.1 PG661 (cntrl) 11.3 10.4 10.3 10.510.3 10.5 10.2  9.7  9.4 PG666 13.4 14.4 14.0 10.1 11.0 20.6 91.0 92.993.5 Human serum, 0 hr PG490 (cntrl) — — — — — — — — 94.9 PG490-88(cntrl) — — — — — — — — 89.2 PG661 (cntrl) — — — — — — — —  7.9 PG666 —— — — — — — — 93.6 Medium only PG490 (cntrl) — — — — — — — — 96.5PG490-88 (cntrl) — — — — — — — — 93.8 PG661 (cntrl) — — — — — — — — 13.6PG666 + medium — — — — — — — — 94.3 Other controls DMSO + Hu — — — — — —— —  7.5 PBS + Hu — — — — — — — —  7.5 Medium — — — — — — — —  7.8

Dose-response data on apoptosis induction by invention compounds PG666(14-ethyl carbamate), PG671 (14-phenyl carbamate) and PG 672(N-methylpiperazinecarbonyl) (carbamate), in comparison to triptolide(PG490), its 14-succinyl ester (PG490-88), and its 14-glutamyl ester(PG661), is given in Table 4. The dose-response data is also representedgraphically in FIG. 2. (Some assays gave a higher apparent backgroundapoptosis than is usually seen, which is assumed to be an artifactisolated to this experiment.)

TABLE 4 Apoptotic Induction by Triptolide Esters and Carbamates in thePresence of Human Serum % apoptotic cells at given concentration (nM)0.03 0.1 0.3 1 3 10 30 100 300 1000 3000 10000 Serum, 48 hr PG666 39.940.7 40.8 41.3 39.8 39.8 39.1 40.2 44.5 88.6 96.8 92.3 PG671 42.5 43.343.9 44.2 43.2 42.4 44.7 43.5 43.1 43.0 43.3 15.4 PG672 42.7 45.2 45.445.9 45.3 46.0 46.8 46.6 42.3 43.7 44.9 63.2 Controls PG490  7.0  6.9 6.8  6.4  7.0  7.1 29.4 90.9 93.0 93.2 94.6 94.2 PG490-88  6.6  6.5 7.0  6.0  6.2  6.2  6.8 30.5 89.6 92.6 92.8 93.9 PG661 38.8 38.2 39.039.2 39.1 39.2 40.3 38.6 36.3 28.7 28.2  5.2 Serum, 0 hr PG666 — — — — —— — — — — — 87.2 PG671 — — — — — — — — — — — 10.2 PG672 — — — — — — — —— — — 47.6 Controls PG490 — — — — — — — — — — — 92.1 PG490-88 — — — — —— — — — — — 82.9 PG661 — — — — — — — — — — —  5.2 Medium PG666 — — — — —— — — — — — 92.6 PG671 — — — — — — — — — — — 13.7 PG672 — — — — — — — —— — — 48.6 Controls PG490 — — — — — — — — — — — 93.4 PG490-88 — — — — —— — — — — — 89.7 PG661 — — — — — — — — — — —  7.3 DMSO + Hu — — — — — —— — — — —  6.7 PBS + Hu — — — — — — — — — — —  6.6

Dose-response data on apoptosis induction by invention compounds PG666(14-ethyl carbamate) and PG688 (14-dimethylaminoethyl carbamate), incomparison to triptolide (PG490) and its 14-succinyl ester (PG490-88),is given in Table 5. The dose-response data is also representedgraphically in FIG. 3.

TABLE 5 Apoptotic Induction by Triptolide Esters and Carbamates in thePresence of Human Serum (48 hrs) % apoptotic cells at givenconcentration (nM) 1 3 10 30 100 300 1000 3000 Human serum PG490 (cntrl) 8.8  8.5  8.6 15.9 86.5 90.7 91.7 93.1 PG490-88  8.6  9.3  8.7  7.823.3 88.4 90.5 91.7 (cntrl) PG688  9.2  9.8  9.4  9.5  9.4  8.7  8.6 8.2 PG666  9.8 10.9 10.4 10.2  9.5 14.9 87.7 91.0 Medium PG490 (cntrl)— — — — — — — 93.7 PG490-88 — — — — — — — 64.8 (cntrl) PG688 13.0 14.012.1 10.9 11.2 11.3 12.1 10.9 PG666 13.9 13.1 13.4 13.0 13.2 14.2 14.192.1 Other controls Medium — — — — — — —  9.1 DMSO + Hu — — — — — — — 9.2 PBS + Hu — — — — — — —  9.1

Inspection of the dose-response data for these compounds shows PG666(14-ethyl carbamate) to be more active than PG688 (4-dimethylaminoethylcarbamate) and PG671 (14-phenyl carbamate) after 48 hr. incubation inhuman serum. PG666 showed equal apoptotic activity to PG490 (triptolide)at roughly a 10-fold higher concentration. TheN-methylpiperazinecarbamate (PG672) showed activity at highconcentrations (FIG. 2), while to the isoglutamyl ester (PG661) showedessentially no activity (FIGS. 1-2).

III. Anticancer Treatment

Triptolide prodrugs have shown effectiveness in cancer treatment invivo. See, for example, coowned PCT Publication No. WO 02/56835, whichis incorporated herein by reference. This document describes highefficacy of a triptolide prodrug, in comparison to 5-FU and CPT-11, instudies with tumor xenografts of the LIT-29 human colon cancer cellline. The triptolide prodrug (a 14-succinate derivative of triptolide)strongly inhibited tumor growth, to a significantly greater degree than5-FU and CPT-11, and induced tumor regression.

The invention thus includes the use of a composition as described hereinto treat cancers, including cancers involving cells derived fromreproductive tissue (such as Sertoli cells, germ cells, developing ormore mature spermatogonia, spermatids or spermatocytes and nurse cells,germ cells and other cells of the ovary), the lymphoid or immune systems(such as Hodgkin's disease and non-Hodgkin's lymphomas), thehematopoietic system, and epithelium (such as skin and gastrointestinaltract), solid organs, the nervous system, and musculo-skeletal tissue.The triptolide prodrugs may be used for treatment of various cancer celltypes, including, but not limited to, breast, colon, small cell lung,large cell lung, prostate, malignant melanoma, liver, kidney,pancreatic, esophogeal, stomach, ovarian, cervical or lymphoma tumors.Treatment of breast, colon, lung, and prostate tumors is particularlycontemplated. Treatment of leukemias is also contemplated. Thecomposition may be administered to a patient afflicted with cancerand/or leukemia by any conventional route of administration, asdiscussed above.

The method is useful to slow the growth of tumors, prevent tumor growth,induce partial regression of tumors, and induce complete regression oftumors, to the point of complete disappearance. The method is alsouseful in preventing the outgrowth of metastases derived from solidtumors.

The compositions of formula I may be administered as sole therapy orwith other supportive or therapeutic treatments not designed to haveanti-cancer effects in the subject. The method also includesadministering the compounds of formula I in combination with one or moreconventional anti-cancer drugs or biologic protein agents, where theamount of drug(s) or agent(s) is, by itself, ineffective to induce theappropriate suppression of cancer growth, in an amount effective to havethe desired anti-cancer effects in the subject. Such anti-cancer drugsinclude actinomycin D, camptothecin, carboplatin, cisplatin,cyclophosphamide, cytosine arabinoside, daunorubicin, doxorubicin,etoposide, fludarabine, 5-fluorouracil, hydroxyurea, gemcitabine,irinotecan, methotrexate, mitomycin C, mitoxantrone, paclitaxel,taxotere, teniposide, topotecan, vinblastine, vincristine, vindesine,and vinorelbine. Anti-cancer biologic protein agents include tumornecrosis factor (TNF), TNF-related apoptosis inducing ligand (TRAIL),other TNF-related or TRAIL-related ligands and factors, interferon,interleukin-2, other interleukins, other cytokines, chemokines, andfactors, antibodies to tumor-related molecules or receptors (such asanti-HER2 antibody), and agents that react with or bind to these agents(such as members of the TNF super family of receptors, other receptors,receptor antagonists, and antibodies with specificity for these agents).

IV. Prodrug Conversion and Cytokine Inhibiting Activity

A. Conversion Assays

As discussed above, the compounds of formula I provide the advantage ofdifferent and sometimes widely varying rates of conversion to parentcompound. Accordingly, prodrugs of formula I can be selected fordifferent conversion rates in human serum/plasma by choosing differentstructural constituents linked via a carbonate or carbamate linkage totriptolide.

Several compounds of formula I were analyzed for their capacity toinhibit IL-2 production in Jurkat human T lymphocyte cells, afterincubation with pooled human serum for 48 hours at 37° C. (see Example20). An ester prodrug, triptolide-14-succinate, designated PG490-88, wasincluded for comparison.

The results of the immunosuppression assay are presented in Table 6. TheIC₅₀ values (column 1) are calculated directly from the data in eachexperiment. The % conversion values (column 2) are calculated as thepercent of the IC₅₀ value produced by triptolide, designated PG490,incubated in the same plasma (i.e. in the same experiment).

TABLE 6 Compound IC₅₀ (nM) Conversion (%) PG490-88 (cntrl) 9 51PG682PTSA 2 97 PG680 3 44 PG681 3 55 PG676 6 84 PG679 12 11 PG682 23 78PG687tris 29 6 PG687 61 2 PG687Na 92 1 PG695 100 2

Again, a broad range of values is shown for the conversion of theprodrugs as evaluated in the IL-2 inhibition assay. This broad range ofconversion values in human serum or plasma indicates that the compoundsof formula I do not share a similar conversion rate under thesecircumstances. This unexpected difference in conversion rates from thesetriptolide prodrugs to triptolide shows that different and widelyvarying rates of conversion can be obtained by making differentlysubstituted prodrugs as described herein.

B. Dose-Response Data

Dose-response data on IL-2 inhibition by invention compounds PG666(14-ethyl carbamate) and PG688 (14-dimethylaminoethyl carbamate), incomparison to triptolide (PG490) and its 14-succinyl ester (PG490-88),is given in Table 7. The dose-response data is also representedgraphically in FIG. 4.

TABLE 7 Inhibition of IL-2 production in Jurkat cells (48 hrs) IL-2pg/mL at given concentration (nM) 0 0.001 0.01 0.1 1 10 100 1000 10000Controls PG490 932.4 929.7 908.6 937.8 835.2 556.1 120.7  62.9  59.2PG490- 838.0 776.4 771.0 809.5 732.4 605.1 317.5  65.9  58.2 88 Com-pounds PG688, 848.5 883.9 754.1 810.4 900.4 796.3 873.3 759.9 459.8serum PG666, 846.0 844.6 799.8 860.6 773.0 819.1 528.0 180.1  63.5 serum

Dose-response data on IL-2 inhibition by invention compounds PG666(14-ethyl carbamate), PG671 (14-phenyl carbamate) and PG672(14-N-methylpiperazinecarbonyl) (carbamate), in comparison to triptolide(PG490), its 14-succinyl ester (PG490-88), and its isoglutamyl ester(PG661), is given in Table 8. The dose-response data is also representedgraphically in FIG. 5.

TABLE 8 Inhibition of IL-2 production in Jurkat cells IL-2 pg/mL atgiven concentration (nM) 0 0.0001 0.001 0.01 0.1 1 10 100 1000 10000Compounds PG666 104.5 94.3 105.1 97.0 92.8 80.0 89.8 33.3 10.0 8.0 PG671117.7 96.4 102.7 99.7 114.7 106.1 90.7 77.9 48.7 8.8 PG672 92.0 103.390.8 99.1 117.1 91.4 99.1 64.6 26.8 8.7 Controls PG490 77.4 80.0 97.283.2 87.1 75.7 25.5 17.8 12.9 22.3 PG490-88 79.0 96.1 83.0 87.5 86.388.2 42.7 14.0 8.4 23.8 PG661 94.9 82.0 102.1 123.6 120.7 98.2 110.3103.6 74.4 68.7

Several of the invention compounds (PG666, 14-ethyl carbamate; PG688,4-dimethylaminoethyl carbamate; PG671, 14-phenyl carbamate; and PG672,N-methylpiperazinecarbamate) showed some level of bioactivity in theseassays (FIGS. 4-5). Again, the isoglutamyl ester (PG661) showed littleor no activity (FIG. 5). PG666 (14-ethyl carbamate) showed equal IL-2inhibitory activity to PG490 (triptolide) at about 10-30 times theactive concentration of PG490.

V. Immunomodulating and Antiinflammatory Treatment

Pharmaceutical compositions comprising compounds of formula I, which areprodrugs of triptolide, are useful in other applications for whichtriptolide has proven effective, e.g. in immunosuppression therapy, asin treating an autoimmune disease, preventing transplantation rejection,or treating or preventing graft-versus-host disease (GVHD).

The method is useful for inhibiting rejection of a solid organtransplant, tissue graft, or cellular transplant from an incompatiblehuman donor, thus prolonging survival and function of the transplant,and survival of the recipient. This use would include, but not belimited to, solid organ transplants (such as heart, kidney and liver),tissue grafts (such as skin, intestine, pancreas, gonad, bone, andcartilage), and cellular transplants (such as cells from pancreas, brainand nervous tissue, muscle, skin, bone, cartilage and liver).

The method is also useful for inhibiting xenograft (interspecies)rejection; i.e. in preventing the rejection of a solid organ transplant,tissue graft, or cellular transplant from a non-human animal, whethernatural in constitution or bioengineered (genetically manipulated) toexpress human genes, RNA, proteins, peptides or other non-native,xenogeneic molecules, or bioengineered to lack expression of theanimal's natural genes, RNA, proteins, peptides or other normallyexpressed molecules. The invention also includes the use of acomposition as described above to prolong the survival of such a solidorgan transplant, tissue graft, or cellular transplant from a non-humananimal.

In another aspect, the invention includes a method of treatment orprevention of graft-versus-host disease, resulting from transplantationinto a recipient of matched or mismatched bone marrow, spleen cells,fetal tissue, cord blood, or mobilized or otherwise harvested stemcells. The dose is preferably in the range 0.25-2 mg/kg body weight/day,preferably 0.5-1 mg/kg/day, given orally or parenterally.

Also included are methods of treatment of autoimmune diseases ordiseases having autoimmune manifestations, such as Addison's disease,autoimmune hemolytic anemia, autoimmune thyroiditis, Crohn's disease,diabetes (Type I), Graves' disease, Guillain-Barre syndrome, systemiclupus erythematosus (SLE), lupus nephritis, multiple sclerosis,myasthenia gravis, psoriasis, primary biliary cirrhosis, rheumatoidarthritis and uveitis, asthma, atherosclerosis, Type I diabetes,psoriasis, and various allergies. In treating an autoimmune condition,the patient is given the composition on a periodic basis, e.g., 1-2times per week, at a dosage level sufficient to reduce symptoms andimprove patient comfort. For treating rheumatoid arthritis, inparticular, the composition may be administered by intravenous injectionor by direct injection into the affected joint. The patient may betreated at repeated intervals of at least 24 hours, over a several weekperiod following the onset of symptoms of the disease in the patient.

Immunosuppressive activity of compounds in vivo can be evaluated by theuse of established animal models known in the art. Such assays may beused to evaluate the relative effectiveness of immunosuppressivecompounds and to estimate appropriate dosages for immunosuppressivetreatment. These assays include, for example, a well-characterized ratmodel system for allografts, described by Ono and Lindsey (1969), inwhich a transplanted heart is attached to the abdominal great vessels ofan allogeneic recipient animal, and the viability of the transplantedheart is gauged by the heart's ability to beat in the recipient animal.A xenograft model, in which the recipient animals are of a differentspecies, is described by Wang (1991) and Murase (1993). A model forevaluating effectiveness against GVHD involves injection of normal F₁mice with parental spleen cells; the mice develop a GVHD syndromecharacterized by splenomegaly and immunosuppression (Korngold, 1978;Gleichmann, 1984). Single cell suspensions are prepared from individualspleens, and microwell cultures are established in the presence andabsence of concanavalin A to assess the extent of mitogenicresponsiveness.

For therapy in transplantation rejection, the method is intendedparticularly for the treatment of rejection of heart, kidney, liver,cellular, and bone marrow transplants, and may also be used in thetreatment of GVHD. The treatment is typically initiated perioperatively,either soon before or soon after the surgical transplantation procedure,and is continued on a daily dosing regimen, for a period of at leastseveral weeks, for treatment of acute transplantation rejection. Duringthe treatment period, the patient may be tested periodically forimmunosuppression level, e.g., by a mixed lymphocyte reaction involvingallogenic lymphocytes, or by taking a biopsy of the transplanted tissue.

In addition, the composition may be administered chronically to preventgraft rejection, or in treating acute episodes of late graft rejection.As above, the dose administered is preferably 1-25 mg/kg patient bodyweight per day, with lower amounts being preferred for parenteraladministration, and higher amounts for oral administration. The dose maybe increased or decreased appropriately, depending on the response ofthe patient, and over the period of treatment, the ability of thepatient to resist infection.

The compounds are also useful as potentiators when administeredconcurrently with another immunosuppressive drug for immunosuppressivetreatments as discussed above. A conventional immunosuppressant drug,such as cyclosporin A, FK506, azathioprine, rapamycin, mycophenolicacid, or a glucocorticoid, may thus be administered in an amountsubstantially less (e.g. 20% to 50% of the standard dose) than when thecompound is administered alone. Alternatively, the triptolide analog andimmunosuppressive drug are administered in amounts such that theresultant immunosuppression is greater than what would be expected orobtained from the sum of the effects obtained with the drug andtriptolide analog used alone. Typically, the immunosuppressive drug andpotentiator are administered at regular intervals over a time period ofat least 2 weeks.

The compositions of formula I are also useful for the treatment ofinflammatory conditions such as asthma, both intrinsic and extrinsicmanifestations. For treatment of asthma, the composition is preferablyadministered via inhalation, but any conventional route ofadministration may be useful. The composition and method may also beused for treatment of other inflammatory conditions, including traumaticinflammation, inflammation in Lyme disease, psoriasis, chronicbronchitis (chronic infective lung disease), chronic sinusitis, sepsisassociated acute respiratory distress syndrome, Behcet's disease,pulmonary sarcoidosis, pemphigus, pemphigoid inflammatory bowel disease,and ulcerative colitis. Triptolide and the present analogs are alsouseful in reducing male fertility.

The compositions of formula I may also be administered in combinationwith a conventional anti-inflammatory drug (or drugs), where the drug oramount of drug administered is, by itself, ineffective to induce theappropriate suppression or inhibition of inflammation.

The dose that is administered is preferably in the range of 1-25 mg/kgpatient body weight per day, with lower amounts being preferred forparenteral administration, and higher amounts being preferred for oraladministration. Optimum dosages can be determined by routineexperimentation according to methods known in the art.

VI. Prodrugs of Triptolide as Substrates for Antibody-Conjugated Enzymes

Triptolide derivatives which are resistant to hydrolysis by humanesterases and proteases may be advantageously employed in antibodydirected enzyme prodrug therapy. In this methodology, an anti-tumorantibody is conjugated to an appropriate enzyme (e.g., carboxypeptidaseG2) and allowed to localize to a tumor, while clearing from normaltissues. A non-toxic prodrug is then delivered, and is activated to atoxic drug specifically by enzyme at the tumor site. (See e.g. Bagshawe1987, 1989, 1993; Bagshawe et al. 1988).

An enzyme that hydrolyzes an oxygen-carbonyl-nitrogen moiety may be usedto convert the less readily converted carbamates of the invention (e.g.PG671, PG672, PG688). Antibody-conjugated enzymes capable of hydrolyzinga carbamate ester bond are known; see e.g. Wentworth et al. 1996.Accordingly, the above carbamates of triptolide may be useful asprodrugs that are significantly less toxic and would be liberated at atumor site in to the presence of antibody-conjugated enzymes.

VII. Therapeutic Compositions

Formulations containing the triptolide analogs of formula I may take theform of solid, semi-solid, lyophilized powder, or liquid dosage forms,such as tablets, capsules, powders, sustained-release formulations,solutions, suspensions, emulsions, ointments, lotions, or aerosols,preferably in unit dosage forms suitable for simple administration ofprecise dosages. The compositions typically include a conventionalpharmaceutical carrier or excipient and may additionally include othermedicinal agents, carriers, or adjuvants. Preferably, the compositionwill be about 0.5% to 75% by weight of a compound or compounds offormula I, with the remainder consisting of suitable pharmaceuticalexcipients. For oral administration, such excipients includepharmaceutical grades of mannitol, lactose, starch, magnesium stearate,sodium saccharine, talcum, cellulose, glucose, gelatin, sucrose,magnesium carbonate, and the like. If desired, the composition may alsocontain minor amounts of non-toxic auxiliary substances such as wettingagents, emulsifying agents, or buffers.

The composition may be administered to a subject orally, transdermallyor parenterally, e.g., by intravenous, subcutaneous, intraperitoneal, orintramuscular injection. For use in oral liquid preparation, thecomposition may be prepared as a solution, suspension, emulsion, orsyrup, being supplied either in liquid form or a dried form suitable forhydration in water or normal saline. For parenteral administration, aninjectable composition for parenteral administration will typicallycontain the triptolide analog in a suitable intravenous solution, suchas sterile physiological salt solution.

Liquid compositions can be prepared by dissolving or dispersing thetriptolide analog (about 0.5% to about 20%) and optional pharmaceuticaladjuvants in a carrier, such as, for example, aqueous saline, aqueousdextrose, glycerol, or ethanol, to form a solution or suspension. Thehigh water solubility of the compounds of formula I make themparticularly advantageous for administering in aqueous solution, e.g. byintraperitoneal injection. Although aqueous solutions are preferred,compositions in accordance with formula I may also be formulated as asuspension in a lipid (e.g., a triglyceride, a phospholipid, or apolyethoxylated castor oil such as “CREMOPHOR EL™”), in a liposomalsuspension, or in an aqueous emulsion.

The compound may also be administered by inhalation, in the form ofaerosol particles, either solid or liquid, preferably of respirablesize. Such particles are sufficiently small to pass through the mouthand larynx upon inhalation and into the bronchi and alveoli of thelungs. In general, particles ranging from about 1 to 10 microns in size,and preferably less than about 5 microns in size, are respirable. Liquidcompositions for inhalation comprise the active agent dispersed in anaqueous carrier, such as sterile pyrogen free saline solution or sterilepyrogen free water. If desired, the composition may be mixed with apropellant to assist in spraying the composition and forming an aerosol.

Methods for preparing such dosage forms are known or will be apparent tothose skilled in the art; for example, see Remington's PharmaceuticalSciences (19th Ed., Williams & Wilkins, 1995). The composition to beadministered will contain a quantity of the selected compound in apharmaceutically effective amount for effecting immunosuppression in asubject.

EXAMPLES

The following examples illustrate but are not intended in any way tolimit the invention.

Example 1 Preparation of a Triptolide Carbamate by Reaction with anIsocyanate (General Procedure A)

A mixture of triptolide, 1 (0.20 mmol, 1.0 eq) and an isocyanate (3.0mmol, 15.0 eq) in N,N-dimethylformamide (DMF, 7.0 ml) is sealed andheated in 54° C. oil bath with stirring. The reaction is monitored withTLC. After the starting material is completely consumed, the reactionmixture is concentrated under vacuum, and the crude product is purifiedwith preparative TLC.

Example 2 Preparation of a Triptolide Carbamate by Reaction withPhosgene and an Amine (General Procedure B)

To a solution of triptolide, 1 (0.325 mmol, 1.0 eq) and4-dimethylaminopyridine (DMAP, 0.0377 mmol, 0.12 eq) in 1,4-dioxane (15ml) is added with stirring pyridine (1.0 ml) and phosgene (˜20% intoluene, 1.19 ml, 2.25 mmol, 6.92 eq) at room temperature undernitrogen. After 1 hour of stirring at room temperature, the reactionmixture is concentrated under vacuum. To the residue is addeddichloromethane (DCM, 15.0 ml) and then the amine (R⁶R⁷NH, 1.0 ml).After 10 minutes of stirring at room temperature, the reaction mixtureis concentrated under vacuum, and the crude product is purified withpreparative TLC.

Example 3 Preparation of a Triptolide Carbonate by Reaction with aChloroformate (General Procedure C)

To a solution of triptolide, 1 (0.33 mmol, 1.0 eq) and4-dimethylaminopyridine (DMAP, 3.92 mmol, 11.9 eq) in dichloromethane(DCM, 15 ml) is added with stirring a chloroformate (2.15 mmol, 6.5 eq)at room temperature under nitrogen. After 24 hours of stirring at roomtemperature, the reaction mixture is concentrated under vacuum, and thecrude product is purified with preparative TLC.

Example 4 Preparation of a Triptolide Carbonate by Reaction withPhosgene and an Alcohol (General Procedure D)

To a solution of triptolide, 1 (0.30 mmol, 1.0 eq) and4-dimethylaminopyridine (DMAP, 3.60 mmol, 12.0 eq) in 1,4-dioxane (15ml) is added with stirring phosgene (−20% in toluene, 0.79 ml, 1.50mmol, 5.0 eq) at room temperature under nitrogen. After 1 hour ofstirring at room temperature, the reaction mixture is concentrated undervacuum. To the residue is added dichloromethane (DCM, 15 ml) and thenthe alcohol (R²OH, 1.0 ml). After stirring at room temperatureovernight, the reaction mixture is concentrated under vacuum, and thecrude product is purified with preparative TLC.

Example 5 Synthesis of Triptolide 14-Ethyl Carbamate (PG666)

Using General Procedure A, the product was obtained in 98.5% yield fromethyl isocyanate and triptolide. Analytical TLC Rf=0.44 (ethylacetate/hexanes/methanol 1:1:0.1). IR (KBr): 3369.6, 2975.6, 2937.6,2878.0, 1753.0, 1719.0, 1686.1, 1676.5, 1524.0, 1517.7, 1509.0, 1458.7,1448.8, 1245.8, 1142.5, 1076.3, 1030.8, 988.1, 944.4, 866.9, 722.6,560.5 cm⁻¹. H¹ NMR (300 MHz, CDCl₃): δ=4.94 (1H, s, 14-CH), 4.68 (2H, s,19-CH₂), 3.83 (1H, d, 11-CH), 3.51 (1H, d, 12-CH), 3.48 (1H, d, 7-CH),3.26 {2H, m, 22-CH₂ (—NCH₂ CH₃)}, 2.70 (1H, m, 5-CH), 2.32 (1H, m,2-CHb), 2.13 (2H, m, 6-CHb and 2-CHa), 1.93 (2H, m, 15-CH and 6-CHa),1.57 (1H, dd, 1-CHb), 1.22 (1H, m, 1-CHa), 1.16 {3H, t, 23-CH₃ (—NCH₂CH₃ )}, 1.07 (3H, s, 20-CH₃), 0.99 (3H, d, 17-CH₃), 0.86 (3H, d, 16-CH₃)ppm. HRMS (FAB) m/z calcd for C₂₃H₃₀NO₇ ⁺ (MH⁺) 432.2022. found432.2016.

Example 6 Synthesis of Triptolide 14-Phenyl Carbamate (PG671)

Using General Procedure A, the product was obtained in 87.0% yield fromphenyl isocyanate and triptolide. Analytical TLC Rf=0.51 (ethylacetate/hexanes/methanol 1:1:0.1). IR (KBr): 3315.3, 2970.4, 2939.5,2878.3, 1751.9, 1676.6, 1600.8, 1543.0, 1534.7, 1443.6, 1314.6, 1215.3,1063.3, 1028.5, 761.0, 693.1 cm⁻¹. H¹ NMR (300 MHz, CDCl₃): δ=7.43 (2H,d, Ar—H), 7.30 (2H, dd, Ar—H), 7.07 (1H, t, Ar—H), 5.04 (1H, s, 14-CH),4.82 (2H, s, 19-CH₂), 3.88 (1H, d, 11-CH), 3.57 (1H, d, 12-CH), 3.52(1H, d, 7-CH), 2.67 (1H, m, 5-CH), 2.33 (1H, d, 2-CHb), 2.17 (2H, m,6-CHb and 2-CHa), 1.96 (2H, m, 15-CH and 6-CHa), 1.58 (1H, dd, 1-CHb),1.25 (1H, m, 1-CHa), 1.08 (3H, s, 20-CH₃), 1.02 (3H, d, 17-CH₃), 0.88(3H, d, 16-CH₃) ppm.

Example 7 Synthesis of Triptolide 14-Dimethylaminoethyl Carbamate(PG688)

Using General Procedure B, the product was obtained in 79.9% yield fromtriptolide, phosgene and N,N-dimethylethylenediamine. Analytical TLCRf=0.45 (ethyl acetate/hexanes/methanol/triethylamine 1.2:0.8:0.2:0.1).IR (KBr): 3380.1, 2969.6, 2827.3, 2780.3, 1753.4, 1720.3, 1675.8,1560.7, 1542.0, 1523.8, 1459.4, 1448.6, 1388.3, 1348.3, 1254.3, 1132.9,1069.9, 1023.7, 888.2, 773.7, 561.0, 522.3 cm⁻¹. H¹ NMR (300 MHz,CDCl₃): δ=5.57 (1H, t, CONH—), 4.94 (1H, s, 14-CH), 4.68 (2H, s,19-CH₂), 3.83 (1H, d, 11-CH), 3.52 (1H, d, 12-CH), 3.48 (1H, d, 7-CH),3.31 {2H, m, 22-CH₂(CONHCH₂ CH₂)}, 2.69 (1H, m, 5-CH), 2.48 {2H, dd,23-CH₂ (CONHCH₂ CH₂ —)}, 2.34 (1H, m, 2-CHb), 2.27 {6H, s, —N(CH₃)₂},2.23-2.13 (2H, m, 2-CHa and 6-CHb), 2.03-1.84 (2H, m, 15-CH and 6-CHa),1.58 (1H, dd, 1-CHb), 1.21 (1H, m, 1-CHa), 1.07 (3H, s, 20-CH₃), 0.99(3H, d, 17-CH₃), 0.85 (3H, d, 16-CH₃) ppm.

Example 8 Synthesis of Triptolide 14-Ethyl Carbonate (PG674)

Using General Procedure C, the product was obtained in 89.6% yield fromethyl chloroformate and triptolide. Analytical TLC Rf=0.58 (ethylacetate/hexanes/methanol 1:1:0.1). IR (KBr): 2972.3, 2938.3, 2879.4,1474.3, 1677.0, 1448.0, 1372.0, 1253.5, 1170.1, 1092.8, 1068.5, 1004.4,962.3, 912.3, 864.6, 786.0, 560.1 cm⁻¹. H¹ NMR (300 MHz, CDCl₃): δ=4.83(1H, s, 14-CH), 4.68 (2H, q, 19-CH₂), 4.25 {2H, qd, 22-CH₂ (—OCH₂ CH₃)},3.82 (1H, d, 11-CH), 3.55 (1H, dd, 12-CH), 3.49 (1H, d, 7-CH), 2.70 (1H,m, 5-CH), 2.32 (1H, m, 2-CHb), 2.19 (2H, m, 6-CHb and 2-CHa), 1.96 (2H,m, 15-CH and 6-CHa), 1.61 (1H, m, 1-CHb), 1.37 {3H, t, 23-CH₃ (—OCH₂ CH₃)}, 1.21 (1H, m, 1-CHa), 1.07 (3H, s, 20-CH₃), 0.99 (3H, d, 17-CH₃),0.86 (3H, d, 16-CH₃) ppm.

Example 9 Synthesis of Triptolide 14-Phenyl Carbonate (PG676)

Using General Procedure C, the product was obtained in 78.8% yield fromphenyl chloroformate and triptolide. Analytical TLC Rf=0.53 (ethylacetate/hexanes/methanol 1:1:0.1). IR (KBr): 2969.7, 2937.6, 1752.1,1676.5, 1442.6, 1265.6, 1210.6, 1021.5, 961.8, 910.7, 774.3, 560.6 cm⁻¹.H¹ NMR (300 MHz, CDCl₃): δ=7.42-7.20 (5H, m, Ar—H), 4.83 (1H, s, 14-CH),4.68 (2H, q, 19-CH₂), 3.83 (1H, d, 11-CH), 3.55 (1H, dd, 12-CH), 3.49(1H, d, 7-CH), 2.68 (1H, m, 5-CH), 2.32 (1H, m, 2-CHb), 2.19 (1H, m,6-CHb and 2-CHa), 1.96 (2H, m, 15-CH and 6-CHa), 1.49 (1H, m, 1-CHb),1.24 (1H, m, 1-CHa), 1.07 (3H, s, 20-CH₃), 0.99 (3H, d, 17-CH₃), 0.86(3H, d, 16-CH₃) ppm.

Example 10 Synthesis of Triptolide 14-Ethoxyethyl Carbonate (PG679)

Using General Procedure D, the product was obtained in 90.2% yield fromtriptolide, phosgene and ethoxyethanol. Analytical TLC Rf=0.49 (ethylacetate/hexanes/methanol 1:1:0.1). IR (KBr): 2974.0, 2935.3, 2876.5,1750.8, 1676.4, 1458.6, 1448.6, 1388.7, 1375.8, 1122.3, 1023.0, 962.3,910.8, 866.1, 784.1, 751.6, 559.7 cm⁻¹. H¹ NMR (300 MHz, CDCl₃): δ=4.83(1H, s, 14-CH), 4.80 (2H, q, 19-CH₂), 4.40 {1H, m, 22-CHb(OCOOCHaHbCH₂)}, 4.27 {1H, m, 22-CHa (OCOOCHaHbCH₂—)}, 3.82 (1H, d,11-CH), 3.68 {2H, m, 23-CH₂ (OCOOCH₂ CH₂ —)}, 3.54 {3H, m, 12-CH and24-CH₂ (—OCH₂ CH₃)}, 3.48 (1H, d, 7-CH), 2.68 (1H, m, 5-CH), 2.31 (1H,m, 2-CHb), 2.18 (2H, m, 2-CHa and 6-CHb), 1.96 (2H, m, 15-CH and 6-CHa),1.58 (1H, dd, 1-CHb), 1.21 {4H, 1-CHa and 25-CH₃ (OCH₂ CH₃ )}, 1.07 (3H,s, 20-CH₃), 0.99 (3H, d, 17-CH₃), 0.85 (3H, d, 16-CH₃) ppm.

Example 11 Synthesis of Triptolide14-(R)-α-Methyl-tert-butoxycarbonylmethyl Carbonate (PG681)

Using General Procedure D, the product was obtained in 76.2% yield fromtriptolide, phosgene and tert-butyl (R)-(+)-lactate. Analytical TLCRf=0.62 (ethyl acetate/hexanes/methanol 1:1:0.1). IR (KBr): 2979.5,2938.3, 2880.6, 1754.6, 1676.9, 1474.0, 1458.1, 1370.1, 1351.6, 1318.0,1264.2, 1165.7, 1136.2, 1116.3, 1074.7, 1031.2, 962.5, 912.6, 866.8,843.6, 786.2, 560.6 cm⁻¹. H¹ NMR (300 MHz, CDCl₃): δ=4.85 {1H, q, 22-CH[OCOOCH(CH₃)CO]}, 4.83 (1H, s, 14-CH), 4.68 (2H, q, 19-CH₂), 3.83 (1H,d, 11-CH), 3.56 (1H, dd, 12-CH), 3.48 (1H, d, 7-CH), 2.65 (1H, m, 5-CH),2.31 (1H, m, 2-CHb), 2.23-2.04 (3H, m, 6-CHb, 2-CHa and 15-CH), 1.93(1H, dd, 6-CHa), 1.59 (1H, dd, 1-CHb), 1.52 {3H, d, 28-CH₃ [OCOOCH(CH₃)CO]}, 1.45 {9H, s, OC(CH₃)₃}, 1.19 (1H, m, 1-CHa), 1.08 (3H, s,20-CH₃), 1.01 (3H, d, 17-CH₃), 0.87 (3H, d, 16-CH₃) ppm.

Example 12 Synthesis of Triptolide 14-Methoxycarbonylmethyl Carbonate(PG680)

Using General Procedure D, the product was obtained in 82.4% yield fromtriptolide, phosgene and methyl glycolate. Analytical TLC Rf=0.45 (ethylacetate:hexanes:methanol 1:1:0.1). IR (KBr): 2967.9, 2882.3, 1751.9,1676.6, 1439.5, 1383.0, 1283.9, 1245.5, 1213.3, 1022.0, 1005.0, 962.1,910.7, 783.1, 560.6, 547.9, 530.6, 521.5, 478.7 cm⁻¹. H¹ NMR (300 MHz,CDCl₃): δ=4.84 (1H, s, 14-CH), 4.80 {1H, d, 22-CHb (OCOOCHaHbCO)}, 4.68(2H, q, 19-CH₂), 4.57 {1H, d, 22-CHa (OCOOCHaHbCO)}, 3.83 (1H, d,11-CH), 3.79 {3H, s, 24-CH₃ (—OCH₃)}, 3.56 (1H, dd, 12-CH), 3.49 (1H, d,7-CH), 2.70 (1H, m, 5-CH), 2.32 (1H, m, 2-CHb), 2.23-2.14 (2H, m, 2-CHaand 6-CHb), 2.07-1.89 (2H, m, 15-CH and 6-CHa), 1.59 (1H, m, 1-CHb),1.23 (1H, m, 1-CHa), 1.08 (3H, s, 20-CH₃), 1.02 (3H, d, 17-CH₃), 0.89(3H, d, 16-CH₃) ppm.

Example 13 Synthesis of Triptolide 14-Dimethylaminoethyl Carbonate(PG682)

Using General Procedure D, the product was obtained in 71.2% yield fromtriptolide, phosgene and dimethylaminoethanol. Analytical TLC Rf=0.24(ethyl acetate:hexanes:methanol:triethylamine 1:1:0.1:0.02). IR (KBr):2969.4, 2824.8, 2772.3, 1751.1, 1676.2, 1671.3, 1655.0, 1473.9, 1466.0,1375.1, 1254.9, 1020.4, 992.6, 962.7, 910.6, 778.9, 557.4, 517.1, 472.4,440.7 cm⁻¹. H¹ NMR (300 MHz, CDCl₃): δ=4.83 (1H, s, 14-CH), 4.68 (2H, s,19-CH₂), 4.34 {2H, m, 22-CH₂ (OCOOCH₂ CH₂N)}, 3.82 (1H, d, 11-CH), 3.55(1H, d, 12-CH), 3.49 (1H, d, 7-CH), 2.75-2.62 {3H, m, 23-CH₂ (OCOOCH₂CH₂ N) and 5-CH}, 2.37 (6H, s, —N(CH₃)₂}, 2.31 (1H, m, 2-CHb), 2.23-2.15(2H, m, 2-CHa and 6-CHb), 2.04-1.89 (2H, m, 15-CH and 6-CHa), 1.58 (1H,dd, 1-CHb), 1.21 (1H, m, 1-CHa), 1.06 (3H, s, 20-CH₃), 0.99 (3H, d,17-CH₃), 0.85 (3H, d, 16-CH₃) ppm. HRMS (FAB) m/z calcd for C₂₅H₃₄NO₈ ⁺(MH⁺) 476.2284. found 476.2289.

Example 14 Synthesis of p-Toluenesulfonate Salt of Triptolide14-Dimethylaminoethyl Carbonate (PG682 PTSA)

With stirring, to a solution of p-toluenesulfonic acid (19.0 mg, 0.10mmol) in H₂O (8.0 ml) was slowly added triptolide 14-dimethylaminoethylcarbonate (PG682) (47.6 mg, 0.10 mmol). After the addition, the solutionwas stirred for another 30 minutes and then lyophilized to yield 60.5 mg(93.4%) of white powder. IR (KBr): 3445.0, 3035.8, 2972.1, 2730.1,1750.9, 1676.1, 1671.9, 1664.8, 1655.4, 1638.1, 1459.3, 1256.2, 1169.3,1121.7, 1033.3, 1010.3, 961.0, 910.7, 817.9, 683.0, 570.4, 479.0 cm⁻¹.H¹ NMR (300 MHz, DMSO-d₆): δ=7.47 (2H, d, Ar—H), 7.10 (2H, d, Ar—H),4.82 (2H, q, 19-CH₂), 4.80 (1H, s, 14-CH), 4.46 {2H, m, 22-CH₂ (OCOOCH₂CH₂N)}, 3.97 (1H, d, 11-CH), 3.73 (1H, d, 12-CH), 3.67 (1H, d, 7-CH),3.44 {2H, m, 23-CH₂ (OCOOCH₂ CH₂ N)}, 2.83 (3H, s, Ar—CH₃), 2.63 (1H, m,5-CH), 2.28 {6H, s, —N(CH₃)₂}, 2.22 (1H, m, 6-CHb), 2.15 (1H, m, 2-CHb),2.09 (1H, m, 2-CHa), 1.98 (1H, m, 1-CHb), 1.90 (1H, m, 15-CH), 1.81 (1H,dd, 6-CHa), 1.30 (1H, m, 1-CHa), 0.91 (3H, s, 20-CH₃), 0.90 (3H, d,17-CH₃), 0.78 (3H, d, 16-CH₃) ppm.

Example 15 Synthesis of Triptolide 14-Hydroxycarbonylmethyl Carbonate(PG687)

Using General Procedure D, the product was obtained in 47.8% yield fromtriptolide, phosgene and glycolic acid. Analytical TLC Rf=0.32 (ethylacetate:hexanes:methanol:acetic acid 1:1:0.1:0.1). IR (KBr): 3416.0,2975.4, 1752.6, 1701.4, 1685.8, 1638.3, 1559.5, 1415.9, 1257.7, 1021.3,810.3, 643.0, 528.0 cm⁻¹. H¹ NMR (300 MHz, MeOH-d₄): δ=4.85 (1H, s,14-H), 4.82 {2H, q, 22-CH₂ (OCOOCH₂ CO)}, 4.46 (2H, q, 19-CH₂), 3.95(1H, d, 11-CH), 3.65 (1H, d, 12-CH), 3.50 (1H, d, 7-CH), 2.78 (1H, m,5-CH), 2.34-2.20 (2H, m, 6-CHb and 2-CHb), 2.08 (1H, m, 15-CH),1.99-1.62 (2H, m, 2-CHa and 6-CHa), 1.50 (1H, dd, 1-CHb), 1.34 (1H, td,1-CHa), 1.04 (3H, s, 20-CH₃), 0.98 (3H, d, 17-CH₃), 0.85 (3H, d, 16-CH₃)ppm. HRMS (FAB) m/z calcd for C₂₃H₂₆NaO₁₀ ⁺ (MNa⁺) 485.1424. found485.1434.

Example 16 Synthesis of Sodium Salt of Triptolide14-Hydroxycarbonylmethyl Carbonate (PG687 Na)

To a solution of NaHCO₃ (5.18 mg, 0.0616 mmol) in H₂O (3.9 ml) wasslowly added triptolide 14-hydroxycarbonylmethyl carbonate (PG687) (28.5mg, 0.0616 mmol) with stirring. After the addition, the solution wasstirred for another 30 minutes and then lyophilized to yield 29.7 mg(99.3%) of white powder. IR (KBr): 2961.4, 2877.2, 1638.1, 1560.8,1551.2, 1412.0, 1261.8, 1021.0, 803.4, 641.0, 530.6, 523.5 cm⁻¹. H¹ NMR(300 MHz, DMSO-d₆): δ=4.82 {2H, q, 22-CH₂ (OCOOCH₂ CO)}, 4.70 (1H, s,14-CH), 4.16 (1H, d, 19-CHb), 3.98 (1H, d, 19-CHa), 3.94 (1H, d, 11-CH),3.69 (1H, d, 12-CH), 3.57 (1H, d, 7-CH), 2.58 (1H, m, 5-CH), 2.22 (1H,m, 6-CHb), 2.11 (1H, m, 2-CHb), 1.97 (2H, m, 2-CHa and 15-CH), 1.81 (1H,m, 6-CHa), 1.49 (1H, m, 1-CHb), 1.30 (1H, m, 1-CHa), 0.92 (3H, s,20-CH₃), 0.90 (3H, d, 17-CH₃), 0.75 (3H, d, 16-CH₃) ppm.

Example 17 Synthesis of Tris(hydroxymethyl)aminomethane Salt ofTriptolide 14-Hydroxycarbonyl-methyl Carbonate (PG687 tris)

To a suspension of triptolide 14-hydroxycarbonylmethyl carbonate (PG687)(8.3 mg, 0.018 mmol) was added a solution oftris(hydroxymethyl)aminomethane (2.17 mg, 0.018 mmol) in H₂O (0.75 ml)with stirring. After the addition, the solution was stirred for another30 minutes and then lyophilized. The powder was dissolved in H₂O (2.0ml) and filtered through a pad of cotton to remove the fine particles.The filtrate was then lyophilized to yield 10.1 mg (96.5%) of whitepowder. IR (KBr): 3364.5 (br), 2975.8, 1750.1, 1581.1, 1413.7, 1349.8,1255.7, 1019.0, 968.5, 911.1, 648.9, 619.6, 561.2, 497.8 cm⁻¹. H¹ NMR(300 MHz, DMSO-ds): δ=4.82 {2H, q, 22-CH₂ (OCOOCH₂ CO)}, 4.70 (1H, s,14-CH), 4.20 (1H, d, 19-CHb), 4.02 (1H, d, 19-CHa), 3.94 (1H, d, 11-CH),3.69 (1H, d, 12-CH), 3.56 (1H, d, 7-CH), 3.20 (6H, s, (HOCH₂ )₃CNH₂},2.61 (1H, m, 5-CH), 2.22 (1H, m, 6-CHb), 2.11 (1H, m, 2-CHb), 1.96 (2H,m, 2-CHa and 15-CH), 1.81 (1H, m, 6-CHa), 1.30 (2H, m, 1-CH₂), 0.91 (3H,s, 20-CH₃), 0.90 (3H, d, 17-CH₃), 0.76 (3H, d, 16-CH₃) ppm.

Example 18 Synthesis of Triptolide 14-tert-Butyl Carbonate (PG695)

To a solution of triptolide (108.1 mg, 0.30 mmol, 1.0 eq) and 4-DMAP(367.0 mg, 3.0 mmol, 10.0 eq) in dichloromethane (15 ml) was added withstirring di-tert-butyl dicarbonate (393.0 mg 1.80 mmol, 6.0 eq) at roomtemperature under nitrogen. After 48 hours of stirring at roomtemperature, methyl alcohol (1.0 ml) was added. The reaction mixture wasconcentrated under vacuum and the crude product was purified withpreparative TLC (ethyl acetate/hexanes/methanol 1:1:0.1) to give 131.3mg (95.1%) of the desired product. Analytical TLC Rf=0.66 (ethylacetate/hexanes/methanol 1:1:0.1). IR (KBr): 2976.7, 2938.5, 1738.2,1676.7, 1444.6, 1394.6, 1370.5, 1335.2, 1278.4, 1254.5, 1160.1, 1118.2,1091.8, 1020.2, 991.6, 962.9, 912.0, 854.4, 786.4, 751.5, 607.2, 558.2,529.3, 478.2 cm⁻¹. H¹ NMR (300 MHz, CDCl₃): δ=4.80 (1H, s, 14-CH), 4.68(2H, q, 19-CH₂), 3.81 (1H, d, 11-CH), 3.53 (1H, d, 12-CH), 3.46 (1H, d,7-CH), 2.69 (1H, m, 5-CH), 2.35 (1H, m, 2-CHb), 2.18 (2H, m, 6-CHb and2-CHa), 1.96 (2H, m, 15-CH and 6-CHa), 1.61 (1H, m, 1-CHb), 1.51 {9H, s,—OC(CH₃)₃}, 1.24 (1H, m, 1-CHa), 1.08 (3H, s, 20-CH₃), 0.99 (3H, d,17-CH₃), 0.86 (3H, d, 16-CH₃) ppm.

Example 19 Apoptosis Assays

A. Incubation of compounds with human serum. Pooled human serum wasstored in aliquots at −80° C. Test compounds were added at 20 mM tothawed human serum in 1.5 ml microfuge tubes and incubated at 37° C. ina water bath for varying periods of time. The test samples were placedon ice until dilution for the bioassay. Controls consisted of thecompounds incubated in complete tissue culture medium (RPMI 1640 mediumplus 5% heat-inactivated fetal calf serum, 1% HEPES, 1% pen/strep, 1%glutamine) rather than human serum.

B. Apoptosis assay of compounds incubated with human serum. Test sampleswere diluted to 1 mM in complete tissue culture medium. Aliquots wereplaced in microculture plates and serial dilutions were prepared so thatthe final concentration would encompass the range of 1 to 10,000 nM withhalf-log increments. Cells from an exponentially expanding culture ofthe Jurkat human T lymphocyte cell line (#TIB-152 obtained from AmericanType Culture Collection, Manassas, Va.) were harvested, washed once bycentrifugation and dilution in complete tissue culture medium, anddiluted to a concentration of 1×10⁶ cells/ml. A volume of 100 μl ofJurkat cells (1×10⁵ cells) was added to wells containing 100 μl of thediluted compounds, and the plates were incubated at 37° C. in a 5% CO₂incubator. After 24 hours, the plates were centrifuged to pellet thecells, and the cells were washed twice with 2% heat-inactivated fetalcalf serum in PBS. To each well, 500 ul of binding buffer was addedaccording to the Annexin V assay procedure (BioVision, Inc., MountainView, Calif.). Next, 5 μl of the fluorescein isothiocyanate (FITC)conjugate of Annexin V (BioVision, Inc.) was added to each well,followed by 5 minutes of incubation in the dark. In some assays,propidium iodide (BioVision, Inc.) was added at this stage to check fornecrotic cells. The contents of the wells were individually transferredinto test tubes, and apoptosis was analyzed using a FACSCalibur flowcytometer (BD Immunocytometry Systems, San Jose, Calif.). Cells positivefor Annexin V binding were considered to be apoptotic, and the data werecalculated as percent apoptotic cells.

C. Comparison of bioactivities after incubation of compounds in humanserum. The data were plotted as the concentration of compound incubatedin serum versus percent apoptotic cells. The concentration of compoundinducing 50% apoptosis (ED₅₀) was calculated from these dose responsecurves. The percent conversion of the test compounds to bioactivecompounds (assumed to be triptolide) was calculated in reference to theresult with triptolide incubated in parallel in human plasma in the sameexperiment, as the percent of the ED₅₀ of the compound compared to thatfor triptolide, which was taken as 100%. This percentage conversion wasused to compare the bioactivity of various compounds after incubation inhuman serum.

Example 20 Immunosuppression Assays

A. IL-2 production assay for activity of compounds incubated with humanserum. Test samples were diluted to 1 mM in complete tissue culturemedium. Aliquots were placed in microculture plates that had been coatedwith anti-CD3 antibody (used to stimulate the production of IL-2 byJurkat cells) and serial dilutions were prepared so that the finalconcentration would encompass the range of 0.001 to 10,000 nM in logincrements. Cells from an exponentially expanding culture of the Jurkathuman T lymphocyte cell line (#TIB-152 obtained from American TypeCulture Collection, Manassas, Va.) were harvested, washed once bycentrifugation and dilution in complete tissue culture medium, anddiluted to a concentration of 2×10⁶ cells/ml. A volume of 50 μl ofJurkat cells (1×10⁵ cells) was added to wells containing 100 μl of thediluted compounds, 50 μl of PMA (10 ng/ml) was added to each well, andthe plates were incubated at 37° C. in a 5% CO₂ incubator. After 24hours, the plates were centrifuged to pellet the cells, 150 μl ofsupernatant was removed from each well, and the samples were stored at−20° C. The stored supernatants were analyzed for human IL-2concentration using the Luminex 100 (Luminex Corporation, Austin, Tex.),Luminex microspheres coupled with anti-IL-2 capture antibody, andfluorochrome-coupled anti-IL-2 detection antibody. The data wereexpressed as ng/ml of IL-2.

B. Comparison of bioactivities after incubation of compounds in humanserum. The data were plotted as the concentration of compound incubatedin serum versus IL-2 concentration. The concentration of compoundinducing a 50% decrease in the IL-2 concentration (IC₅₀) was calculatedfrom these dose response curves. The percent conversion of the testcompounds to bioactive compounds (assumed to be triptolide) wascalculated in reference to the result with triptolide incubated inparallel in human plasma in the same experiment, as the percent of theIC₅₀ of the compound compared to that for triptolide, which was taken as100%. This percentage conversion was used to compare the bioactivity ofvarious compounds after incubation in human serum.

1. A method of inducing cell death, comprising administering to asubject in need of such treatment, in a pharmaceutically acceptablevehicle, an effective amount of a triptolide prodrug, or apharmaceutically acceptable salt thereof, having the structure I:

where X¹ is OR¹, and X² and X³ are H; and OR¹ is O—(C═O)—Z, where Z isselected from the group consisting of: —OR², —O—Y—(C═O)—OR³, —O—Y—NR⁴R⁵,—NR⁴R⁵, —NR³—Y—(C═O)—OR³, and —NR³—Y—NR⁴N⁵; wherein Y is a divalentalkyl, alkenyl or alkynyl group having up to six carbon atoms; R² isselected from alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl,hydroxyalkyl, alkoxyalkyl, aryloxyalkyl, and acyloxyalkyl; each R³ isindependently selected from hydrogen and R²; and R⁴ and R⁵ areindependently selected from hydrogen, alkyl, alkenyl, alkynyl,cycloalkyl, cycloalkenyl, aryl, aralkyl, hydroxyalkyl, alkoxyalkyl,aryloxyalkyl, and acyloxyalkyl, or R⁴ and R⁵ taken together form a 5- to7-member heterocyclic ring whose ring atoms are selected from the groupconsisting of carbon, nitrogen, oxygen and sulfur, wherein said ringatoms include at most 3 heteroatoms.
 2. The method of claim 1, whereinOR¹ is-selected from the group consisting of: O—(C═O)—NR⁴R⁵,O—(C═O)—NR³—Y—(C═O)—OR³, and O—(C═O)—NR³—Y—NR⁴N⁵.
 3. The method of claim1, wherein Z is —NR⁴R⁵.
 4. The method of claim 1, wherein each of thegroups defined as R², R³, R⁴, and R⁵, when selected from alkyl, alkenyl,and alkynyl, have up to six carbon atoms, with the proviso that R² isnot alkyl; when defined as cycloalkyl, have 3 to 7 carbon atoms; whendefined as cycloalkenyl, have 5 to 7 carbon atoms; and when selectedfrom aralkyl, hydroxyalkyl, alkoxyalkyl, aryloxyalkyl, and acyloxyalkyl,have alkyl components with up to six carbon atoms.
 5. The method ofclaim 4, wherein each of R², R³, R⁴, and R⁵ is independently selectedfrom the group consisting of alkyl having up to six carbon atoms, aryl,aralkyl, and alkoxyalkyl.
 6. The method of claim 5, wherein R² has up tosix carbon atoms.
 7. The method of claim 1, wherein said treatment istreatment of leukemia.
 8. The method of claim 1, wherein said treatmentis treatment of a solid tumor selected from the group consisting ofpancreatic cancer and melanoma.
 9. A method of effectingimmunosuppression, comprising administering to a subject in need of suchtreatment, in a pharmaceutically acceptable vehicle, an effective amountof a compound having the structure I as defined in claim
 1. 10. Themethod of claim 9, wherein said immunosuppression comprises inhibitionof transplant rejection.
 11. The method of claim 10, wherein saidimmunosuppression comprises inhibition of a kidney transplant rejection.12. The method of claim 10, wherein said immunosuppression comprisesinhibition of a bone marrow transplant rejection.
 13. The method ofclaim 9, wherein said immunosuppression comprises inhibition ofgraft-versus-host disease (GVHD).
 14. The method of claim 9, whereinsaid immunosuppression comprises treatment of an autoimmune disease. 15.The method of claim 14, wherein said autoimmune disease is selected fromthe group consisting of Addison's disease, autoimmune hemolytic anemia,autoimmune thyroiditis, Crohn's disease, diabetes (Type I), Graves'disease, Guillain-Barre syndrome, systemic lupus erythematosus (SLE),lupus nephritis, multiple sclerosis, myasthenia gravis, psoriasis,primary biliary cirrhosis, rheumatoid arthritis and uveitis, asthma,atherosclerosis, Type I diabetes, psoriasis, and various allergies.